Evolution of Debris‐Flow Initiation Mechanisms and Sediment Sources During a Sequence of Postwildfire Rainstorms
AffiliationUniv Arizona, Dept Geosci
MetadataShow full item record
PublisherAMER GEOPHYSICAL UNION
CitationTang, H., McGuire, L. A.,Rengers, F. K., Kean, J. W.,Staley, D. M., & Smith, J. B. (2019). Evolution of debris-flow initiation mechanisms and sediment sources during a sequence of post wildfire rainstorms. Journal of Geophysical Research: Earth Surface, 124,1572–1595. https://doi.org/10.1029/2018JF004837
RightsThis article is a U.S. Government work and is in the public domain in the USA.
Collection InformationThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at firstname.lastname@example.org.
AbstractWildfire alters vegetation cover and soil hydrologic properties, substantially increasing the likelihood of debris flows in steep watersheds. Our understanding of initiation mechanisms of postwildfire debris flows is limited, in part, by a lack of direct observations and measurements. In particular, there is a need to understand temporal variations in debris-flow likelihood following wildfire and how those variations relate to wildfire-induced hydrologic and geomorphic changes. In this study, we use a combination of in situ measurements, hydrologic monitoring equipment, and numerical modeling to assess the impact of wildfire-induced hydrologic and geomorphic changes on debris-flow initiation during seven postwildfire rainstorms. We predict the impact of hillslope erosion on debris-flow initiation by combining terrestrial laser scanning surveys of a hillslope burned during the 2016 Fish Fire with numerical modeling of sediment transport throughout a 0.12-km(2) basin in southern California. We use measurements of sediment thickness within the channel to constrain numerical experiments and to assess the role of channel sediment supply on debris-flow initiation. Results demonstrate that debris flows initiated during rainstorms where hillslopes contributed minimally to the event sediment yield and suggest that large inputs of sediment from rill and gully networks are not essential for runoff-generated debris flows. Simulations suggest that both the gradual entrainment of sediment and the mass failure of channel bed sediment can increase sediment concentration to levels associated with debris flows. Finally, postwildfire debris-flow initiation appears closely linked to the same rainfall intensity-duration threshold despite temporal changes in the sediment source, initiation processes, and hydraulic roughness.
NotePublic domain article
VersionFinal published version
SponsorsU.S. Geological Survey (USGS) Landslide Hazards Program